1. Field of the Invention
The present invention relates to a duplicated light source module.
It is sometimes required to duplicate a light source in a transmitter, so as to construct a highly reliable optical communication system. In such a case, rays of light from both light sources are preliminarily adapted to be coupled to an optical transmission line. In the initial stage of operation of a system, one of the light sources is used. In the event that this light source is troubled or will be possibly troubled during the operation, the other light source is selected instead. Thus, system failure is prevented.
Further, there is another case that it is required to enlarge an output of a light source device by multiplexing a light source. For example, in a fiber type optical amplifier recently in practical application, such enlargement of the output of the light source device is effective in requiring high-energy pumping light.
2. Description of the Related Art
Conventionally, a laser diode (LD) module is known as an example of a light source device for use in an optical communication system or the like. The LD module is constituted of a laser diode (LD) chip, an end portion of an optical fiber, and a lens for optically coupling the LD chip to the end portion of the optical fiber. These members are arranged in predetermined positional relationship to each other. Duplication of such an LD module is effected by utilizing the fact that light to be emitted from the LD chip is substantially linearly polarized light. That is, two LD modules each having a polarization plane maintaining fiber as an optical fiber for outputting light are used, and rays of light output from the polarization plane maintaining fibers of the two LD modules are made enter a single optical fiber through a polarization beam splitter. Accordingly, in duplicating a light source device in the prior art, the light source device becomes large in size because of the necessity of use of the polarization plane maintaining fibers, for example.
Further, the use of a birefringent element functioning as an optical isolator is known as an optical device for optically coupling a pair of optical fibers (U.S. Pat. No. 4,548,478).